The invention generally relates to a system and technique to improve a well stimulation process.
For purposes of preparing a well for production, a perforating gun typically is lowered down into a well""s casing wellbore to form perforation tunnels. These perforation tunnels extend through the casing, cement grout and into the formation(s) that are exposed by the drilling of the wellbore. In this manner, the perforating gun includes shaped charges that when detonated produce the corresponding perforation tunnels. The perforation tunnels allow reservoir fluids to flow from the formations through the perforation tunnels and into the well bore. Subsequent to the perforating operation by the perforating gun, a fracturing operation may be performed for purposes of increasing the well""s ability to produce fluids from the reservoirs to maximize production.
In a typical fracturing operation, a fracturing fluid is introduced into the well and then pressurized. This pressurization of fluid creates fractures in the subterranean rock. The pumping of fluids down the well and into these fractures transports particulates, called proppant, into the fractures, and hence, when the fluid pressure is released the fractures do not close but remain open due to the proppant particles now being in the rock fractures. Likewise, fracturing fluids can contain chemicals and particles that etch the face of the newly created hydraulic fractures, or the chemicals in the hydraulic fracture process otherwise increase the reservoir""s ability to conduct reservoir fluids to the well bore such that once the hydraulic pressure is released, the hydraulic fractures remain as improved paths of fluid conductivity to the reservoir.
The proppant-laden fluid may be quite expensive, and typically, the fracturing operation that uses this proppant-laden fluid is a one-time operation for the well. Thus, it is important for the fracturing to be effective. The effectiveness of the fracturing operation typically depends on a plurality of parameters, including the quality of the perforation tunnels, the ability of the adjacent reservoir rock to accept fracture fluids and the rock""s fluid loss characteristics. It is common practice to perform a fluid efficiency test, which does not include the proppant particles, to evaluate the fracture fluids fluid loss characteristics to the reservoir rock. During the fluid efficiency test, the pressure of the test fluid at the surface of the well is observed. In this manner, increases and decreases in the surface pressure of the test fluid may be monitored before and after introduction to assess the general fluid efficiency of the hydraulic fracture fluid design as it relates to the in-situ rock properties leak off properties.
Based on the assessment provided by the fluid efficiency test, the reservoir rock may be subsequently treated in-situ before pumping of the proppant laden fracture fluids. Such a technique may save expenses related to fracturing operations cost as a higher than expected fluid loss rate or spurt fluid loss discovered in the fluid efficiency pumping test can be accommodated by redesigning the proppant-laden fracturing fluid prior to the fracturing operation.
A potential difficulty that is associated with the above-described techniques is that the various perforation tunnels or zones of the well cannot be precisely evaluated as to if they are taking fluid or how much fluid, as the surface pressure measurement only provides a general assessment of the rock""s leak off or spurt losses to the fluid used in the fluid efficiency test.
Alternatively, for a better resolution of where fluids are injected, radioactive fluids or solids may be mixed with the fluid used in the fluid efficiency test, and gamma ray logging may be subsequently used to obtain a more detailed evaluation of the fluid injection points by detecting the radioactive material. This radioactive tracer technique is not commonly used in fluid efficiency testing for two reasons. The first reason is that the use of radioactive materials is not something a prudent operator wishes to do on a frequent basis owing to the many regulatory and health and safety issues involved with the use and transport of these materials. And secondly, radioactive tracer technique does not indicate the relative volumes of fluids injected at any depth. Hence, the art of doing radioactive tracer injection on fluid efficiency tests is not commonly practiced. It is however practiced in the subsequent hydraulic fracture treatment where radioactive materials are mixed with the proppant-laden fluids and injected into the well. The subsequent gamma ray logs reveal the locations of the radioactive-tagged proppant. Therefore, this method of tagging the proppant during the pumping of proppant is not proactive and does not allow for one to adjust the injection profile prior to pumping the expensive proppant material.
Thus, there is a continuing need to address one or more of the problems stated above.
In an embodiment of the invention, a technique that is usable with a subterranean well includes introducing a fluid into the well in connection with a fluid efficiency test. The technique also includes measuring a temperature versus depth distribution along a section of the well in response to the introduction of the fluid.
Advantages and other features of the invention will become apparent from the following drawing, description and claims.